Electrical control device



Jan. 28, 1930. c. E. vAwTER ELECTRICAL CONTROL DEVICE Filed March 15, 1926 2 Sheets-Sheet l lNVENTOR ZM W BY ` ATTORNEY l C Jan. 28, 1930. C. E. AWTER 1,744,995

ELECTRICAL CONTROL DEVICE Filed March l5, 1926 2 Sheets-Sheet 2 INVENTOR ATTORNEY Patented Jan. 28, 1930 U TATES CHARLES E. VAWTER, OF PHILADELPHA,

IO RADIO PATENTS CORPORATON, OF NEW YORK,

EENNSE'LVANA, ASSIGNOR 0F ONE-HALF ELECTRICAL CONTROL DEVICE Application iled March 15, 1926. Serial No. 94,683.

My invention relates to electrical control devices and particularly to a system or method of controlling the flow of a varying electric current between a plurality of points. The principal object of my invention is to provide an improved means for controlling thc tube oscillations in a radio amplifier' system by regulating the character and amount of a neutralizing variable current supplied to the grid circuit of one of the amplifier tubes.

Since my improved controlling device, although useful for many purposes, is particularly suitable for controlling or preventing the oscillations which are frequently set up in the tubes of a radio a pliier system, l will describe my invention as applied to this particular purpose.

lt is well lrnown that where several stages of radio frequency amplification are eniployed, some of the energy of any one of the plate circuits may be fed back to the Grid circuit of the same tube or of the preceding tubes by induction or capacity in the circuits themselves. Unless some method is employed for controlling the energy thus fed back to the grid circuitof a tube, oscillations will be set up in the tube to such an extent as to cause disagreeable sounds in the phones or loud speaker. The energy which causes this disagreeable effect is supplied through some unintended coupling between the grid and the plate circuits of the tubes. This coupling may be caused by magnetic action between transformers located too close together, or it may be caused by the internal resistance of the plate batteries being too high.

It has been proposed therefore to supply energy to the grid circuits with a view to neutralizing or eliminating the currents which cause the undesirable oscillations of the ampliiier tubes. My invention relates particularly to an improved method of accomplishing this result. I have provided a simple device whereby a closely regulated varying current can be supplied to a grid circuit to neutralize the forces which would otherwise cause the tube to oscillate. This improved device, in its simplest form, consists of two condensers of low capacity, each connected in series with a resistance element. rl`he two resistance elements are interconnected and adapted to be connected to the grid circuit of one of the amplifier units. The two condensers are adapted to be connected to successive plate circuits ofthe amplifier. One of the resistance elements is variable and the necessary adjustment of the device can be effected by adjusting this variable resistance element. The amplifier' with which my improved device is to be employed, should be of such a character that the currents in successive plate circuits are out of phase or, to be more exact, of opposite phase. This condition naturally exists where the amplifier units are resistance or impedance coupled. rlhe same condition may be brought about in a transformer coupled amplifier system by reversing the secondary connections of the transformers with respect to the primary connections.

My improved controlling device is preferably made in the form hereinafter described. The characteristic features of this form are the provision of separate condenser elements having a common dielectric strip, and the arrangement of a plurality of resistance elements including at least one variable resistance element between two recessed plates which virtually form a casing for all of the elements. A suitable device for adjusting the variable resistance, projects from between the two recessed plates and suitable tabs or terminals are provided for connecting the resistance and condenser elements in any desired manner.

The various objects and advantages of my invention will be apparent upon considering the following detailed description which is to be considered in conjunction with the accomnanying drawings in which Figure l is a perspective view of one einbodiment of my improved control device.

Figure 2 is a plan view of one section of the device shown in Figure l.

Figure 3 is a plan view of the other section of the device of Figure 1, showing the resistance elements in place.

Figure 4 is a longitudinal section view of the device shown in Figure l.

Figure 5 is a transverse section view of this device taken on a plane corresponding with that indicated at 5 5 in Figure 2.

Figure 6 is a circuit diagram of a radio circuit illustrating one application of the control device shown in the preceding figures.

Figure 7 is a diagram of another radio circuit showing a similar application of my invention.

Figure 8 may be considered as a circuit diagram for the electrical control device shown in Figures 1 to 5, inclusive.

Figure 9 is a circuit diagram of a modified form of the device and Figure 10 is another circuit diagram for another embodiment of the control device.

Following the plan mentioned above of describing my invention as applied to a radio amplifying system, I wish to first direct attention to Figure 6. Figure 6 includes a common'two-stage radio frequency amplifier, the vacuum tubes being shown at 1. In this system of tuned radio frequency amplification, the successive amplifier units are coupled through the variable inductance elements 2 and 3 which are used in tuning the circuits.

As pointed out above, the energy fed back into the grid circuit of the first amplifier tube has a tendency to produce undesirable oscillations within this tube. This ordinarily occurs unless some means is provided for neutralizing the current which represents this energy. My improved method of bringing about this result consists in connecting the grid 4 of the first tube to the plate circuits of two or more succeeding tubes, this connection being effected throuO'h condensers and resistance elements. At 2least one condenser or resistance element should be variable so as to permit the necessary adjustment and I prefer to provide a variable resistance because of the difhculties involved in making variable condensers having the desired capacity and for the further reason that it is cheaper to employ a variable resistance. In Figure 6, I have shown two fixed condensers 5 and 6 each separately connected to one of the plate circuits of the second and third tubes. Condenser number 5 is shown connected to the plate 7 of the second tube by means of the conductor 8 and the condenser 6 is in like manner connected to the plate 9 of the third tube by means of the conductor 10. A fixed resistance element 11 is shown connected in series with the conductor 5 and a corresponding variable resistance element or unit 12 is connected in series With the condenser 6. The two resistance elements are interconnected and connected to the grid 4 of the first tube by means of leads 13, 14 and 15. The amplifier system is such that the current in the plate circuit of the third tube is of opposite phase to that of the plate circuit in the second tube. In other words, at

" any given instant, the current flowing through plate 9 is of opposite sign with respect to the current flowing through the plate 7. It will be noted that the plates 7 and 9 are interconnected through the condensers 5 and 6 and the resistance elements 11 and 12, all of these parts being connected in series. It follows from this that a current will flow through these condensers and resistance elements between the plates 7 and 9 and it also follows that the instantaneous potential of that portion of the series circuit which is connected to grid 4 depends upon the adjustment of the variable resistance 12. Current will flow from the two plate circuits, which may be represented by the numerals 7 and 9, to the grid 4 and the proportion of this current supplied by either one of these elements will depend upon the adjustment of the variable resistance 12, assuming that the two condensers 5 and 6 are of' equal capacity and that the total resistance of each oi' the ltwo resistance elements is the same.

I have found that by employing the control system just described, it is possible to supply enough positive or negative energy as the case may be to the grid 4 to neutralize t-he current resulting from any unintended coupling of the first grid circuit with the other portions of the amplifier system. In practice I have found that the system works very well if the two condensers 5 and 6 eacii have a capacity of .0001 M. F., if the fined resistance element 11 has a resistance of 2 megohms and if the variable resistance ias a resistance range from .1 to .10 megohms.

In Figure 7, I have illustrated another common typerof radio frequency amplifier.

his is similar to that shown in Figure 6, the principal difference being that transformers 2 and 3 have been substituted for the variable inductances 2 and 3 of Figure 6. Tuning may be effected by means of variable condensers shown at 16. The grid 4 of the first tube is shown connected to the plates 7 and 9 of the two succeeding tubes through resistances 11 and 12 and condensers 5 and 6 similar to those shown in Figure 6. At 17 I have shown in dotted lines a condenser which may be used in place of either one of the condensers 5 and 6. I have done this merely to bring out the fact that the method of interconnecting the resistance elements and the condensers can be varied without eX- ceeding the scope of the invention. The important consideration is to have the two plate circuits represented by 7 and 9 interconnected through a condenser and a condenser should be interposed between these circuits and the grid 4 of the first tube. The resistance elements may be connected between the condensers and the plates or between the condensers and the grid as shown in Figure 6. The two resistance elements 11 and 12 may be considered as a single element having an lili) intermediate tap which is connected to the grid of the first tube.

In Figure 8 I have illustrated the control system by itself. This is substantially the same as that shown in Figures 6 and 7 in connection with a radio amplifying system. The two fixed condensers are shown at and 6 and the two resistance elements are shown at 1l and 12. The two condensers are shown connected to points B and C and the two resistances are interconnected and connected to the point- A. It is to be understood that this system can be employed for purposes other than in connection with radio amplifiers. It is of use wherever it is desired to control the supply of current to one point from two other points having different instantaneous potentials. This condition is represented by the positive and negative signs shown at B and C respectively and it will be understood that by adjusting the variable resistance 12, the amount of positive current supplied to the point A may be varied with respect to the amount of negative current owing through the condenser 6 and the resistance 11. By positive and negative currents, I, of course, refer to instantaneous values.

In Figure 9, I have shown the two resistance elements as combined in a single resistance unit- 18 having a pick-off or adjustable tap 19. The other parts of this system are the saine as those shown in Figure 8 and it will be understood that the adjustment is effected by simply moving` the tap 10 toward one end or the other of the resistance unit 18.

In Figure 10,1 have shown a similar system for controlling the supply of current to one point A from a plurality of points B, C, D and E. Each of the points B, C, D and E is connected to the point A through a fixed condenser and a resistance element. The condensers are shown at 5, 6, and 2l and the resistance elements at l2, l1, 22 and 23. The resistance element l2 is variable so as to provide a means for regulating the current flow. The current supplied to the points B, C, D and E from any sources should be such that some of these currents are out o f phase with the remaining currents. I have attempted to illustrate this condition by showing positive and negative signs at the points B and D, and C and E, respectively.

In Figures l to 5, inclusive, I have shown one physical embodiment of my improved electrical control device. The device shown in these iigures comprises two plates 24 and 25 preferably made of insulating material, arranged in contact with each other and clamped together by means of a plurality of screws 26. The adjacent faces of these two plates are provided with recesses 27 and 28 and these are formed in such a manner that the recesses in one of the plates mate with those in the opposite plate to form cavities adapted to receive resistance elements. A metal pla-te 29 is secured to one end of the plate 25 by means of screws 30 and to the corresponding end of plate 24 by means of screws 31. A conducting strip 32 extends from plate 29 between the two plates 24 and 25 and projects out at the far end as shown at 33. A binding post 34 may be provided on this projecting portion of the strip 32. Two metal plates 35 and 36 carrying binding posts 37 and 38 are carried by the upper plate 25 and form parts of condenser elements arranged between the plates 24 and 25. A single piece 39 of mica or other dielectric material extends across the two metal strips 35 and 36; and corresponding metal strips 40 and 41 are carried by the plate 24, opposite the strips 35 and 36. This arrangement provides two condensers side by side having a common strip of dielectric material. I prefer this construction because in this way it is a relatively easy matter to make two condensers of substantially the same capacit-y. One condenser element consists of the strip 35, the dielectric strip 39 and the strip 40, and the other condenser element comprises the metal strip 36, the dielectric strip 39 and the metal strip 4l.

Referring to Figure 3, I have shown a fixed resistance element 42 fitting in a recess 28. A coil spring 42, or an equivalent yielding conducting member, serves to electrically connect one end of the resistance unit 42 with the metal plate 29 and to force the resistance unit toward the metal strip 4l so as to establish an electrical connection between these parts. The fixed resist-ance element 42 may consist of a tube of insulating material such as fiber board, containing a resistance paste and having metal end terminals 43. This type of resistance unit is of the well-known form commonly employed as a grid leak. At 44 I have illustrated a variable resistance unit which may consist of a suitable casing containing a plurality of discs of resistance material and a threaded rod 45 connected to a knob 46. The knob 46 may be mounted in the plate 29 as will be readily understood upon referring to the drawings. A convenient method of mounting this device in a radio set is to secure the plate 29 to the inside of the front panel of the radio cabinet with the shaft 45 projecting through this panel.

Figure 9 may be considered as a circuit or connection diagram for the device shown in Figures l to 5, inclusive. The binding posts 37 and 38 may be considered as connected to the points C and B respectively of Figure 8 and the binding posts 34 may be considered as connected to the point A. The resistance units 42 and 44 correspond with the resistance elements 1l and l2, respectively, of Figure 8. These resistance units 42 and 44 are interconnected by means of the metal plate 29 and the variable resistance unit 44 plunger actuated by a screwis shown connected to an extension 40 of the metal strip 40 by means of a threaded projection 44 secured to the resistance unit. The other resistance unit 42 is shown pressed against the metal condenser strip 4l by means of the spring 42.

I prefer to make the plates 24 and 25 eX- actly alike as shown inFigures 2 and 3, because this lowers the manufacturing cost. My improved device can be easily assembled by simply placing the several parts in position as shown in Figures 2 and 3 and then laying the two plates 24 and 25 together asI shown in Figure l and inserting the screws 25, 30 and 31. The necessary adjustment of the variable resistance unit can be effected by simply turning the knob 46, which has the effect of compressing or releasing the resistance plates of the Variable resistance unit to decrease or increase, as the case may be, the effective resistance of this unit.

It is toV be understood that my invention is not confined to the particular details illustrated and described but includes such modifications thereof as fall within the scope of the appended claims.

I claim:

l. An electrical control device for regulating the flow of varying current between three points, two of which are in circuits carrying currents out of phase with each other, comprising two fixed condensers, means for connecting each condenser to one of said two points, a variable resistance, and means for connecting the condensers and the resistance to the third point with a portion of the resistance in series with the condensers.

2. An electrical control device for regulating the flow of varying current between three points, two of which are in circuits carrying currents out of phase with each other, comprising two fixed condensers, two resistance elements, at least one of which is variable, and means for connecting each of said elements in series with one of the said condensers,

for connecting each condenser to one of said` and for connecting each resistance two points i whereby the said element to the third point,

two points are interconnected through the twov condenser-s and the resistance elements.

3. In a radio amplifier, the combination with a plurality of interconnected amplifier units having successive plate circuits carrying currents of opposite phase, of means for controlling tube oscillations, comprising two condensers, a variable resistance, and con-- nections therefor forming a divided circuit extending between the grid circuit of one tube y and the plate circuits of two succeeding tubes, with the resistance in series withthe condensers, whereby these two plate circuits are interconnected through the condensers.

4. In a radio amplifier, the combination with a plurality of interconnected amplifier units having successive plate circuits carrying currents of opposite phase, of means for controlling tube oscillations, comprising two condensers, two resistance units one of which is Variable, and connecting means therefor forming a divided circuit extending between the grid circuit of one tube and the plate circuits of the two succeeding tubes, with each resistance unit in series with one of the condensers, substantially as described.

5. In a radio amplier, the combination with a plurality of interconnected amplifier units having successive plate circuits carrying currents of opposite phase, of means for controlling tube oscillations, comprising two fixed condensers, separate resistance units one of which is variable, electrically connected in series with each condenser, and meansfor Y connecting the two resistance units to the grid of one tube and means for separately connecting the two condensers to the plates of the two succeeding tubes.

6. In a radio amplifier, the combination with a plurality of interconnected amplifier units having successive plate circuits carrying currents of opposite phase, of means for controlling tube oscillations, comprising a plurality of fixed condensers, sep arate fixed resistance elements electrically connected in series with cach condenser except one, a variable resistance element electrically connected in series with this one condenser, means for connecting all of the resistance elements to the grid circuit of one tube, and means for separately connecting the several condensers to successive plate circuits, substantially as described.Y

In testimony whereof I aiiiX my signature.

CHARLES E. VWTTER. 

